you would need the electronic schematic diagram for each motherboard (which manufacturers do not release), a multimeter, an oscilloscope, specialized soldering equipment. Its not an easy thing to do. You can fix some old motherboards if they have leaking capacitors, and replace visibly damaged components. But no, there is no manual to fix all motherboard problems. Your best bet would be to try get a job at one of the motherboard manufacturers repairing faulty boards if that is what you want to do for a job.